1. Field
The present invention relates to an optical device, and more particularly, to a lens assembly and an optical system including the same.
2. Description of the Related Art
Lens assemblies used in optical devices, in particular, lens assemblies used in mobile phones, digital cameras, or the like, are required to be precisely manufactured in order to secure high resolution thereof. As cameras become smaller in size and as pixel integration of solid imaging devices increases, the performance improvement and precision management of the lens assemblies become more important.
In general, lens assemblies are manufactured by inserting a plurality of unit lenses into a lens barrel. At this time, central axes (the arrangement) of the unit lenses are determined according to the concentricity and precision of the lens barrel. However, the concentricity, flatness, or the like of the lens barrel is not relatively precise (in general, the concentricity and flatness of the lens barrel is equal to or less than 10 μm), and thus, there is a high possibility that the central axes of the unit lenses are not consistent with each other. Thus, a decenter problem occurs, which results in a deterioration of the performance and resolution of a camera. As the number of pixels of a camera increases and as the size of a lens assembly decreases, problems due to the decenter may become more serious.
FIG. 1 is a cross-sectional view illustrating a lens assembly according to the related art.
Referring to FIG. 1, a first lens L1, a second lens L2, and a third lens L3 are inserted into a lens barrel BR1. A valid lens region serving as an actual lens exists at the center of each of the first lens L1, the second lens L2, and the third lens L3, and a flange part exists at an edge of each of them. Both surfaces of the flange part are flat. A first spacer SP1 is provided between the flange part of the first lens L1 and the flange part of the second lens L2, and a second spacer SP2 is provided between the flange part of the second lens L2 and the flange part of the third lens L3. Both surfaces of the first spacer SP1 come into close contact with the flange parts of the first lens L1 and the second lens L2. Similarly, both surfaces of the second spacer SP2 come into close contact with the flange parts of the second lens L2 and the third lens L3. The first lens L1, the second lens L2, and the third lens L3 are fitted into grooves provided in the lens barrel BR1, respectively, and a back ring R1 is finally fitted into and attached to an inlet of the lens barrel BR1 so as to fix the first lens L1, the second lens L2, and the third lens L3.
In the structure shown in FIG. 1, the central axes (the arrangement) of the unit lenses L1, L2, and L3 are greatly influenced by the concentricity, precision, or the like of the lens barrel BR1. Therefore, when the lens barrel BR1 is not precisely manufactured, a decenter problem wherein the central axes of the unit lenses L1, L2, and L3 are not consistent with each other may occur.